U.S. patent application number 13/002358 was filed with the patent office on 2011-05-05 for low surface energy adhesive.
This patent application is currently assigned to 3M Innovation Properties Company. Invention is credited to Zhong Chen, Megan P. Lehmann, Jingjing Ma, Michael L. Tumey, Dong-Wei Zhu.
Application Number | 20110104486 13/002358 |
Document ID | / |
Family ID | 41040282 |
Filed Date | 2011-05-05 |
United States Patent
Application |
20110104486 |
Kind Code |
A1 |
Ma; Jingjing ; et
al. |
May 5, 2011 |
LOW SURFACE ENERGY ADHESIVE
Abstract
Adhesives suitable for use with low surface energy materials are
described. The adhesive contain an acrylic copolymer, a high glass
transition temperature tackifier and a low glass transition
temperature tackifier. The acrylic copolymer is the reaction
product of a first alkyl(meth)acrylate having at least 5 carbon
atoms in the alkyl group, a second alkyl(meth)acrylate having 1 to
4 carbon atoms in the alkyl group, and a vinyl carboxylic acid.
Both tackifiers have a Tg greater than the Tg of the acrylic
copolymer. The high glass transition temperature tackifier has a Tg
of at least 20.degree. C. and the low glass transition temperature
tackifier has a Tg of less than 0.degree. C.
Inventors: |
Ma; Jingjing; (Cottage
Grove, MN) ; Chen; Zhong; (Woodbury, MN) ;
Lehmann; Megan P.; (Stillwater, MN) ; Tumey; Michael
L.; (St Paul, MN) ; Zhu; Dong-Wei; (Shoreview,
MN) |
Assignee: |
3M Innovation Properties
Company
|
Family ID: |
41040282 |
Appl. No.: |
13/002358 |
Filed: |
June 10, 2009 |
PCT Filed: |
June 10, 2009 |
PCT NO: |
PCT/US09/46841 |
371 Date: |
January 3, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61077745 |
Jul 2, 2008 |
|
|
|
Current U.S.
Class: |
428/355AC ;
428/522; 524/502; 525/55 |
Current CPC
Class: |
C09J 133/08 20130101;
C09J 7/385 20180101; B32B 7/12 20130101; Y10T 428/2891 20150115;
C09J 133/02 20130101; C08K 3/36 20130101; Y10T 428/31935 20150401;
C08K 5/01 20130101; C09J 165/02 20130101; B32B 2405/00 20130101;
C09J 193/04 20130101; B32B 2255/26 20130101; C08L 2666/02 20130101;
C09J 133/08 20130101; C08L 2666/02 20130101 |
Class at
Publication: |
428/355AC ;
525/55; 428/522; 524/502 |
International
Class: |
C08L 33/10 20060101
C08L033/10; B32B 27/36 20060101 B32B027/36; B32B 7/12 20060101
B32B007/12; C09B 67/00 20060101 C09B067/00 |
Claims
1. An adhesive comprising: a) an acrylic copolymer comprising the
reaction product of i) a first alkyl (meth)acrylate, wherein the
alkyl group of the first alkyl (meth)acrylate comprises at least 5
carbon atoms; ii) a second alkyl(meth)acrylate, wherein the alkyl
group of the second alkyl (meth)acrylate comprises 1 to 4 carbon
atoms; and iii) a vinyl carboxylic acid; and b) a high Tg tackifier
having a glass transition temperature of at least 20.degree. C.;
and c) a low Tg tackifier having a glass transition temperature of
no greater than 0.degree. C., wherein the glass transition
temperatures of the high Tg tackifier and the low Tg tackifier are
greater than the glass transition temperature of the acrylic
copolymer.
2. The adhesive according to claim 1, wherein the weight ratio of
the first alkyl (meth)acrylate to the second alkyl (meth)acrylate
is between 3:1 and 1:3.
3. The adhesive according to claim 1, wherein the acrylic copolymer
comprises at least 3% by weight and no greater than 8% by weight of
the vinyl carboxylic acid.
4. The adhesive according to claim 1, wherein the adhesive
comprises 40 to 60% by weight total tackifier content based on the
total weight of the acrylic copolymer, the high Tg tackifier and
the low Tg tackifier.
5. The adhesive according to claim 1, wherein the adhesive
comprises 35 to 45% by weight of the high Tg tackifier based on the
total weight of the acrylic copolymer, the high Tg tackifier and
the low Tg tackifier.
6. The adhesive according to claim 1, wherein the adhesive
comprises 2 to 13% by weight of the low Tg tackifier based on the
total weight of the acrylic copolymer, the high Tg tackifier and
the low Tg tackifier.
7. The adhesive according to claim, further comprising a
crosslinker.
8. The adhesive of claim 7, wherein the crosslinker is a covalent
crosslinker selected from the group consisting of bisamides,
epoxies, and melamines.
9. The adhesive of claim 7, wherein the crosslinker is an ionic
crosslinking agent, wherein the ionic crosslinking agent is
selected from the group consisting of multifunctional amines, metal
oxides, and organo-metallic chelating agents.
10. The adhesive according to claim 1, further comprising an
additional component selected from the group consisting of fillers,
dyes, pigments, antioxidants, UV-stabilizers, fumed silica,
nanoparticles, and surface-modified nanoparticles.
11. The adhesive according to claim 1, wherein the glass transition
temperature of the adhesive is no greater than 260 K, as calculated
using the Fox Equation.
12. An adhesive article comprising a first substrate and an
adhesive according to claim 1 bonded to the substrate.
13. The adhesive article of claim 12, wherein the adhesive is
directly bonded to the first substrate.
14. The adhesive article of claim 12, wherein the adhesive is
bonded to a second substrate.
15. The adhesive article of claim 12, wherein the first substrate
is a low surface energy substrate having a surface energy of no
greater than 35 millinewtons per meter.
16. The adhesive of claim 1, wherein (a) the weight ratio of the
first alkyl (meth)acrylate to the second alkyl (meth)acrylate is
between 3:1 and 1:3; and (b) the acrylic copolymer comprises at
least 3% by weight and no greater than 8% by weight of the vinyl
carboxylic acid.
17. The adhesive of claim 16, wherein the adhesive comprises (c) 40
to 60% by weight total tackifier content based on the total weight
of the acrylic copolymer, the high Tg tackifier and the low Tg
tackifiers; (d) 35 to 45% by weight of the high Tg tackifier based
on the total weight of the acrylic copolymer, the high Tg tackifier
and the low Tg tackifiers; and (e) 2 to 13% by weight of the low Tg
tackifier based on the total weight of the acrylic copolymer, the
high Tg tackifier and the low Tg tackifiers.
18. The adhesive of claim 17, wherein the adhesive further
comprises a crosslinker.
19. An adhesive article comprising a first substrate and the
adhesive according to claim 17 bonded to the substrate.
20. The adhesive article of claim 19, wherein the first substrate
is a low surface energy substrate having a surface energy of no
greater than 35 millinewtons per meter.
Description
FIELD
[0001] The present disclosure relates to acrylic adhesives,
particularly adhesives suitable for bonding to low surface energy
substrates. Generally, the adhesives include both a high glass
transition temperature tackifier and a low glass transition
temperature tackifier.
SUMMARY
[0002] Briefly, in one aspect, the present disclosure provides an
adhesive comprising an acrylic copolymer, a high Tg tackifier
having a glass transition temperature of at least 20.degree. C.;
and a low Tg tackifier having a glass transition temperature of no
greater than 0.degree. C., wherein the glass transition
temperatures of the high Tg tackifier and the low Tg tackifier are
greater than the glass transition temperature of the acrylic
copolymer. The acrylic copolymer comprises the reaction product of
a first alkyl (meth)acrylate, wherein the alkyl group of the first
alkyl (meth)acrylate comprises at least 5 carbon atoms; a second
alkyl(meth)acrylate, wherein the alkyl group of the second alkyl
(meth)acrylate comprises 1 to 4 carbon atoms; and a vinyl
carboxylic acid; and
[0003] In some embodiments, the alkyl group of the first
alkyl(meth)acrylate comprises 8 carbon atoms. In some embodiments,
the alkyl group of the second alkyl(meth)acrylate comprises 1 or 2
carbon atoms. In some embodiments, the alkyl group of the second
alkyl(meth)acrylate comprises 4 carbon atoms.
[0004] In some embodiments, the weight ratio of the first alkyl
(meth)acrylate to the second alkyl (meth)acrylate is between 0.7:1
and 1:0.7 e.g., between 0.8:1 and 1:0.8, e.g., between 0.9:1 and
1:0.9. In other embodiments, the weight ratio of the first alkyl
(meth)acrylate to the second alkyl (meth)acrylate is at least 2:1,
e.g., at least 3:1. In still other embodiments, the weight ratio of
the second alkyl (meth)acrylate to the first alkyl (meth)acrylate
is at least 2:1, e.g., at least 3:1.
[0005] In some embodiments, the vinyl carboxylic acid is selected
from the group consisting of acrylic acid, methacrylic acid,
itaconic acid, maleic acid, fumaric acid, and
.beta.-carboxyethylacrylate. In some embodiments, the acrylic
copolymer comprises at least 3% by weight, e.g., at least 4% by
weight of the vinyl carboxylic acid. In some embodiments, the
acrylic copolymer comprises no greater than 10% by weight, e.g., no
greater than 8% by weight, e.g., no greater than 5% by weight of
the vinyl carboxylic acid. In some embodiments, the acrylic
copolymer comprises between 4 and 5% by weight of vinyl carboxylic
acid, inclusive.
[0006] In some embodiments, the adhesive comprises 40 to 60% by
weight total tackifier content based on the total weight of the
acrylic copolymer, the high Tg tackifier and the low Tg tackifier.
In some embodiments, the adhesive comprises 50 to 55% by weight
total tackifier content based on the total weight of the acrylic
copolymer, the high Tg tackifier and the low Tg tackifier.
[0007] In some embodiments, the adhesive comprises 35 to 45% by
weight, e.g., 41 to 43% by weight, of the high Tg tackifier based
on the total weight of the acrylic copolymer, the high Tg tackifier
and the low Tg tackifier. In some embodiments, the high Tg
tackifier is selected from the group consisting of terpene phenolic
resins, terpenes, rosin esters, aliphatic-modified C5 to C9
hydrocarbons, and aromatic-modified C5 to C9 hydrocarbons. In some
embodiments, the high Tg tackifier has a weight average molecular
weight of 500 to 1500 gm/mole, e.g., 500 to 1000 gm/mole, e.g., 500
to 800 gm/mole.
[0008] In some embodiments, the adhesive comprises 2 to 13% by
weight, e.g., 4 to 6% by weight of the low Tg tackifier based on
the total weight of the acrylic copolymer, the high Tg tackifier
and the low Tg tackifier. In some embodiments, the low Tg tackifier
is selected from the group consisting of terpenes, rosin esters,
aliphatic-modified C5 to C9 hydrocarbons, and aromatic-modified C5
to C9 hydrocarbons. In some embodiments, the low Tg tackifier has a
weight average molecular weight of 300 to 1000 gm/mole, e.g., 300
to 800 gm/mole, e.g., 300 to 500 gm/mole.
[0009] In some embodiments, the adhesive further comprises a
crosslinker, e.g., covalent crosslinker(s) and/or ionic
crosslinking agent(s). In some embodiments, the adhesive also
comprises at least one additional component selected from the group
consisting of fillers, dyes, pigments, antioxidants,
UV-stabilizers, fumed silica, nanoparticles, and surface-modified
nanoparticles.
[0010] In some embodiments, the glass transition temperature of the
adhesive is less than 252 K, as measured by differential scanning
calorimetry.
[0011] In another aspect, the present disclosure provides an
adhesive article comprising a first substrate and an adhesive
according to the present disclosure bonded to the substrate. In
some embodiments, the substrate is a low surface energy substrate
having a surface energy of no greater than 35 millinewtons per
meter.
[0012] The above summary of the present disclosure is not intended
to describe each embodiment of the present invention. The details
of one or more embodiments of the invention are also set forth in
the description below. Other features, objects, and advantages of
the invention will be apparent from the description and from the
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 illustrates an exemplary adhesive article according
to some embodiments of the present disclosure.
DETAILED DESCRIPTION
[0014] Generally, adhesives, e.g., pressure sensitive adhesives,
including acrylic adhesives are well-known. The use of tackifiers
and plasticizers to modify the performance of adhesives is also
known. However, although individual components of an adhesive
formula may be known, the selection of a specific combination of
components and their relative amounts in order to achieve specific,
desired end-use requirements remains a significant challenge.
[0015] Adhesion to low surface energy materials is one example of a
long-felt need in the art of adhesive formulation. While there are
adhesives that provide acceptable levels of performance, there is
on ongoing need for more options to meet this key requirement.
[0016] The present inventors have discovered that by selecting both
specific kinds and ratios of monomers in the formation of an
acrylic copolymer, and combining such copolymers with both a high
glass transition temperature and a low glass transition temperature
tackifier, acrylic adhesives with a relatively high acid content
can be formulated to provide excellent adhesion to low surface
energy surfaces. This surprising result is contrary to conventional
thinking in the art of adhesive formulation, where it has been
believed that low acid content is critical to obtaining good
adhesion to low surface energy substrates.
[0017] Generally, the adhesives of the present disclosure comprise
an acrylic copolymer, at least one high glass transition
temperature tackifier and at least one low glass transition
temperature tackifier. In some embodiments, the adhesive also
includes a crosslinking agent. Optionally, other components typical
of adhesive formulations may also be present such as fillers, dyes,
pigments, antioxidants, UV-stabilizers and the like.
[0018] Generally, the acrylic copolymer comprises the reaction
product of a mixture of a first alkyl (meth)acrylate, a second
alkyl(meth)acrylate, and a vinyl carboxylic acid. As used herein,
"(meth)acrylate" refers to an acrylate and/or methacrylate. For
example, butyl (meth)acrylate refers to butyl acrylate and/or butyl
methacrylate. In some embodiments, the mixture may also include a
crosslinking agent.
[0019] The alkyl group of the first alkyl (meth)acrylate contains
at least 5 carbon atoms. In some embodiments, this alkyl group
contains no greater than 8 carbon atoms. In some embodiments, the
alkyl group of the first alkyl (meth)acrylate has eight carbon
atoms, e.g., isooctyl (meth)acrylate and/or 2-ethylhexyl
(meth)acrylate.
[0020] The alkyl group of the second alkyl (meth)acrylate contains
no greater than 4 carbon atoms. In some embodiments, the acrylic
polymer includes at least one alkyl (meth)acrylate having an alkyl
group of 4 carbon atoms, e.g., butyl (meth)acrylate. In some
embodiments, the alkyl group of at least one alkyl (meth)acrylate
contains 1-2 carbon atoms, e.g., methyl acrylate and/or ethyl
acrylate.
[0021] Exemplary vinyl carboxylic acids that may be useful in some
embodiments of the present disclosure include acrylic acid,
methacrylic acid, itaconic acid, maleic acid, fumaric acid, and
.beta.-carboxyethylacrylate. Generally, the acrylic copolymers of
the present disclosure comprise at least 3% by weight, in some
embodiments, at least 4% by weight of the vinyl carboxylic acid
based on the total weight of the alkyl (meth)acrylates and the
vinyl carboxylic acids. In some embodiments, the acrylic polymer
comprises no greater than 10% by weight, in some embodiments, no
greater than 8% by weight, and, in some embodiments, no greater
than 5% by weight of the vinyl carboxylic acid. In some
embodiments, the acrylic polymer comprises 4-5% by weight of vinyl
carboxylic acid based on the total weight of the alkyl
(meth)acrylates and the vinyl carboxylic acids.
[0022] Generally, tackifiers useful in the adhesive compositions of
the present disclosure are materials that are compatible with the
acrylic copolymer to which they are added and have a glass
transition temperature (Tg) greater than the Tg of the acrylic
copolymer. In contrast, a plasticizer is compatible with the
acrylic copolymer but has a Tg less than the Tg of the acrylic
copolymer. Although the actual Tg varies depending on the
formulation of the acrylic copolymer, the Tg of acrylic copolymers
typically less than -20.degree. C., e.g., less than -30.degree. C.,
less than -40.degree. C., or even less than -50.degree. C.
[0023] The adhesives of the present disclosure include at least two
tackifiers, a high Tg tackifier and a low Tg tackifier. The high Tg
tackifier has a Tg of at least 20.degree. C. and is typically a
solid at room temperature. Exemplary high Tg tackifiers include
terpenes, aliphatic- or aromatic-modified C5 to C9 hydrocarbons,
and rosin esters. In some embodiments, lower molecular weight
hydrocarbons may be preferred, as compatibility with the acrylic
copolymer decreases as the molecular weight of the hydrocarbon
increases. In some embodiments, the weight average molecular weight
(Mw) of the high Tg tackifier is between 500 and 2000 gm/mole. In
some embodiments, the Mw of the high Tg tackifier is no greater
than 1500, in some embodiments, in some embodiments, no greater
than 1000, or even no greater than 800 gm/mole.
[0024] The low Tg tackifier has a glass transition temperature of
no greater than 0.degree. C., in some embodiments, no greater than
-10.degree. C., or even no greater than -20.degree. C. Such
materials are generally liquids at room temperature. There is no
particular lower limit on the glass transition temperature of the
low Tg tackifier, except that it must be greater than the Tg the
acrylic copolymer. In some embodiments, the Tg of the low Tg
tackifier is at least 10.degree. C. greater, at least 20.degree. C.
greater, or even at least 30.degree. C. greater than the Tg of the
acrylic copolymer. Generally, lower molecular weight compounds may
be preferred, as compatibility with the acrylic copolymer decreases
as the molecular weight of the increases. Exemplary low Tg
tackifiers include terpene phenolic resins, terpenes, aliphatic- or
aromatic-modified C5 to C9 hydrocarbons, and rosin esters. In some
embodiments, the weight average molecular weight (Mw) of the low Tg
tackifier is between 300 and 1500 gm/mole. In some embodiments, the
Mw of the low Tg tackifier is no greater than 1000, in some
embodiments, no greater than 800, or even no greater than 500
gm/mole.
[0025] Typically, acrylic copolymer-based adhesives require little
or no tackifiers to achieve desired pressure-sensitive adhesive
properties. In contrast, the adhesives of the present disclosure
generally comprise 40 to 60% by weight (wt. %) total tackifier
content, based on the total weight of all tackifiers divided by the
total weight of the acrylic copolymer and all tackifiers. In some
embodiments, the adhesives comprise at least 45 wt. %, and, in some
embodiments, at least 50 wt. % total tackifier content. In some
embodiments, the adhesives comprise no greater than 55 wt. % total
tackifier content.
[0026] In some embodiments, the adhesives comprise 35 to 45 wt. %
of the high Tg tackifier. In some embodiments, the adhesives
comprise at least 40 wt. % of the high Tg tackifier. In some
embodiments, the adhesives comprise no greater than 44 wt. % of the
high Tg tackifier. In some embodiments, the adhesives comprise 41
to 43 wt % of the high Tg tackifier.
[0027] In some embodiments, the adhesives comprise 2 to 13 wt. % of
the low Tg tackifier. In some embodiments, the adhesives comprise
no greater than 10 wt. %, e.g., no greater than 7 wt. % of the low
Tg tackifier. In some embodiments, the adhesives comprise at least
3 wt. %, and, in some embodiments, at least 4 wt. % of the low Tg
tackifier. In some embodiments, the adhesives comprise 3 to 7 wt. %
(4 to 6 wt. %) of the low Tg tackifier.
[0028] In some embodiments, the adhesives of the present disclosure
comprise 35 to 45 wt. % of the high Tg tackifier and 2 to 13 wt. %
of the low Tg tackifier. In some embodiments, the adhesives
comprise 40 to 44 wt. % (e.g., 41 to 43 wt. %) of the high Tg
tackifier and 3 to 7 wt. % (e.g., 4 to 6 wt. %) of the low Tg
tackifier.
[0029] Generally, the relative amounts of the first alkyl
(meth)acrylate and the second alkyl (meth)acrylate can be varied
depending on the specific monomers chosen and the desired
properties. In some embodiments, the weight ratio of the first
alkyl (meth)acrylate to the second alkyl (meth)acrylate is between
4:1 and 1:4, e.g., between 3:1 and 1:3. In some embodiments, the
weight ratio of the first alkyl (meth)acrylate to the second alkyl
(meth)acrylate is about 1:1. For example, in some embodiments, the
ratio is between 0.7:1 and 1:0.7, e.g., between 0.8:1 and 1:0.8, or
even between 0.9:1 and 1:0.9. In other embodiments the ratio of the
first alkyl (meth)acrylate to the second alkyl (meth)acrylate is at
least 2:1, in some embodiments, at least 2.5:1, or even at least
3:1. In some embodiments, the ratio of the first alkyl
(meth)acrylate to the second alkyl (meth)acrylate is between 2:1
and 3:1, inclusive. In still other embodiments, the ratio of the
second alkyl (meth)acrylate to the first alkyl (meth)acrylate is at
least 2:1, in some embodiments, at least 2.5:1, or even at least
3:1. In some embodiments, the ratio of the second alkyl
(meth)acrylate to the first alkyl (meth)acrylate is between 2:1 and
3:1, inclusive.
[0030] In some embodiments, the adhesives of the present disclosure
may contain a crosslinking agent. Generally, any suitable
crosslinking agent may be used. Exemplary crosslinking agents
include covalent crosslinkers such as bisamides, epoxies, and
melamines; and ionic crosslinking agents such as multi-functional
amines, metal oxides, and organo-metallic chelating agents (e.g.,
aluminum acetylacetonate). The amount of crosslinking agent
included depends on well-understood factors such as the desired
degree of crosslinking and the relative effectiveness of the
crosslinking agent in the particular system. For example, in some
embodiments, adhesives of the present disclosure comprise 0.05 to
0.15 wt. % (e.g., 0.08 to 0.14 wt. %) of a bisamide crosslinker
based on the weight of the acrylic copolymer. In some embodiments,
adhesives of the present disclosure comprise 0.2 to 0.8 wt. %
(e.g., 0.2 to 0.5 wt. %) of aluminum acetylacetonate crosslinker
based on the weight of the acrylic copolymer.
[0031] The adhesives of the present disclosure may contain other
common components known for use in adhesives such as dyes,
pigments, UV-stabilizers, fillers and the like. Exemplary fillers
include calcium carbonate, carbon black, and fumed silica. In some
embodiments, nanoparticles, e.g., silica nanoparticles may be
included. In some embodiments, surface-modified nanoparticles may
be included.
[0032] Generally, the glass transition temperature of a mixture of,
e.g., an acrylic copolymer and one or more tackifiers and/or
plasticizers can be calculated using the Fox Equation, i.e.:
1/Tg=.SIGMA.Wi/Tgi. In this equation, Tg is the glass transition
temperature of the mixture, Wi is the weight fraction of component
i in the mixture, and Tgi is the glass transition temperature of
component i, and all glass transition temperatures are in Kelvin
(K). Alternatively, the glass transition temperature can be
measured in a variety of known ways, including, e.g., through
differential scanning calorimetry (DSC).
[0033] In some embodiments, the addition of the high Tg tackifier
and the low Tg tackifier to the acrylic copolymer is sufficient to
raise the glass transition temperature of the resulting adhesive to
no greater than 252 K, as measured by DSC. In some embodiments, the
glass transition temperature is no greater than 260 K, as
calculated using the Fox Equation.
Examples
[0034] General procedure for the preparation of the acrylic
copolymer of acrylic copolymer (AC-1). To a bottle were added 48.0
grams of 2-ethyl hexyl acrylate (2-EHA, obtained from Dow Chemical
Co.), 4.5 grams of butyl acrylate (BA), and 4.5 grams of acrylic
acid (AA, obtained from BASF Corp.) The bottle also contained 177
grams of ethyl acetate (EtOAc, a solvent) and 0.200 grams of
VAZO-67 (an azonitrile polymerization initiator obtained from
DuPont). This mixture was purged with nitrogen to remove all oxygen
and the bottle was then sealed. This sealed bottle was placed in a
water bath and heated at 58.degree. C. for 24 hours. The resulting
sample was further diluted with an additional 56 grams of EtOAc.
The final sample was a clear, viscous solution. The percent solids
(determined by drying the sample at 105.degree. C. for 3 hours) and
the intrinsic viscosity (IV, 0.25 g/dL in EtOAc) were measured and
results are summarized in Table 1.
[0035] Acrylic copolymers AC-2 to AC-6 were made in similar process
by varying monomer concentrations, by adding toluene (Tol) as
polymerization solvent in addition to ethyl acetate, and adjusting
the polymerization temperature, as summarized in Table 1.
TABLE-US-00001 TABLE 1 Description of acrylic copolymers AC-1 to
AC-6. % I.V., Sample 2-EHA/BA/AA Solvents (wt. ratio) Temp. Solids
g/dL AC-1 48/47.5/4.5 EtOAc 58.degree. C. 29.1 1.40 AC-2
48/47.5/4.5 EtOAc 58.degree. C. 29.1 1.47 AC-3 48/47.5/4.5
EtOAc/Tol (50/50) 60.degree. C. 39.1 0.76 AC-4 48/47.5/4.5
EtOAc/Tol (75/25) 60.degree. C. 43.2 1.13 AC-5 49/48/3 EtOAc
60.degree. C. 28.6 1.43 AC-6 25/69/6 EtOAc/Tol (60/40) 60.degree.
C. 39.4 0.83
[0036] Adhesive Compounding and Sample Preparation.
[0037] Materials used to prepare the following adhesive samples are
summarized in Table 2; wherein Tg is the glass transition
temperature, Tsoft is the softening temperature, Mw is the
weight-average molecular weight, and Mn is the number-average
molecular weight.
TABLE-US-00002 TABLE 2 Materials used to prepare adhesives. Mol. Wt
Tg Tsoft (Daltons) Material Description .degree. C. .degree. C. Mw
Mn Source Foral 85LB High Tg tackifier 42 80-88 -- -- Hercules Inc.
SP-553 High Tg 73 110-120 -- -- Schenectady tackifier International
ESCOREZ 2520 Low Tg -22 20-25 450 320 ExxonMobil tackifier Chemical
STAYBELITE Low Tg -18 20-25 -- -- Eastman Ester 3-E tackifier
Chemical SYLVAREZ Low Tg -20 22-28 450 330 Arizona TR A-25
tackifier Chemical GLISSOPAL Plasticizer -60 NA 1000 1600 Exxon
Mobil 1000 (G1000) Chemical PYCAL 94 Plasticizer -65 NA 270 270
Uniquema
[0038] The detailed adhesive compositions for Comparative Examples
CE-1 to CE-4, and Examples 1 to 26 are listed in Table 3. All
ingredients except the bisamide crosslinker were added to a glass
jar. Toluene was added to make solution of 37% to 40% solids. The
jar was put on a roller overnight for mixing. Bisamide crosslinker
was added into the jar right before coating.
[0039] The adhesive solution was coated on a 51 micron (2 mil)
polyester film backing (HOSTAPHAN 3SAB available from Mitsubishi
Polyester Film, Inc., Greer, S.C.) using a 15 cm (6 inch) wide
knife coater. The coater gap was set to give a 51 micron (2.0 mil)
thick adhesive layer after drying. The sample was dried in an oven
at 71.degree. C. (160.degree. F.) for 10 to 15 minutes. The dried
sample was covered with a release liner and stored in controlled
environment (temperature and humidity) room before testing.
[0040] Samples were cut to size and tested according to the
following test methods.
[0041] 90 Degree Peel Adhesion. Peel adhesion testing was performed
as described in the ASTM International standard, D3330, Method F,
with a 1.3 cm.times.20 cm (1/2 in..times.8 in.) test specimen using
an IMASS SP-200 slip/peel tester (available from IMASS, Inc.,
Accord, Mass.). The test panels included stainless steel (SS, 304,
18 gauge stainless steel, bright annealed finish, available from
ChemInstruments, Inc., Fairfield, Ohio), polypropylene (PP, natural
polypropylene panels available from QUADRANT Engineering Plastics
Products USA, Inc., Reading, Pa.), high density polyethylene (HDPE,
PROTEUS natural high density polyethylene available from QUADRANT
Engineering Plastics Products USA, Inc., Reading, Pa.), polymethyl
methacrylate (PMMA, PLEXIGLAS MCM clear panels available from
Altuglas International, Philadelphia, Pa.), polycarbonate (PC,
LEXAN, clear panels available from SABIC Innovative Plastics,
Pittsfield, Mass.), and acrylonitrile-butadiene-styrene (ABS,
general purpose, hair-cell finish panels available from Spartech
Plastics, Clayton, Mo.). The peel tests were performed after a 15
minute dwell time on the test panel, unless otherwise stated. The
average peel adhesion force required to remove the tape from the
panel was measured in ounces and is expressed in Newtons/decimeter
(N/dm).
[0042] 180 Degree Peel Adhesion. Peel adhesion testing was
performed as described in the ASTM International standard, D3330,
Method A, with a 1.3 cm.times.20 cm (1/2 in..times.8 in.) test
specimen using an IMASS SP-200 slip/peel tester available from
IMASS, Inc., Accord, Mass. The test panels were polypropylene (PP,
natural polypropylene panels available from QUADRANT Engineering
Plastics Products USA, Inc., Reading, Pa.). The peel tests were
performed after a 15 minute dwell time on the test panel, unless
otherwise stated. The average peel adhesion force required to
remove the tape from the panel was measured in ounces and is
expressed in Newtons/decimeter (N/dm).
[0043] Static Shear at 70.degree. C. Static shear holding power
testing was performed as described in the ASTM International
standard, D3654, Procedure A, with a 1.3 cm.times.2.5 cm (1/2
in..times.1 in.) test specimen and a 500 g load using an oven at
70.degree. C. (158.degree. F.). The test panels were stainless
steel (SS, 304, 18 gauge stainless steel, bright annealed finish,
available from ChemInstruments, Inc., Fairfield, Ohio). Time to
failure in minutes was recorded. If no failure was observed after
10,000 minutes, the test was stopped and a value of 10,000+ minutes
was recorded.
[0044] All samples showed excellent shear at 70.degree. C. using a
stainless steel panel. The shear test for each sample was
terminated after 10,000 minutes as no failure occurred. As
summarized in Table 3, Comparative Examples CE-1 to CE-4 comprise
only an acrylic copolymer and one or more high Tg tackifiers.
Although these adhesives show good adhesion to a high surface
energy stainless steel panel, they generally had poor adhesion to
polypropylene, a low surface energy (LSE) substrate. In contrast,
the adhesive compositions of Examples 1 to 22, which comprise both
at least one high Tg tackifier and at least one low Tg tackifier,
generally provided significantly improved adhesion to the low
surface energy polypropylene panel while maintaining good adhesion
to the high surface energy stainless steel panel.
TABLE-US-00003 TABLE 3 Adhesive descriptions and test results.
Acrylic copolymer Tackifiers (wt. %) wt. % High Tg Low Tg
90.degree. peel Copoly. in wt. % SP- FORAL SYL. (N/dm) Ex. I.D.
adh. AA 553 85LB A-25 Bisamide wt. % SS PP CE-1 AC-4 63.4 4.5 27.0
9.6 0.0 0.15 84 14 CE-2 AC-4 60.0 4.5 37.2 2.8 0.0 0.1 112 10 CE-3
AC-4 60.0 4.5 37.2 2.8 0.0 0.2 83 7 CE-4 AC-1 50.0 4.5 0.0 50.0 0.0
0.15 129 38 1 AC-4 50.0 4.5 0.0 48.2 1.8 0.2 109 42 2 AC-4 50.0 4.5
0.0 48.2 1.8 0.1 129 50 3 AC-4 50.0 4.5 0.0 28.0 22.0 0.1 95 67 4
AC-4 60.0 4.5 0.0 34.8 5.2 0.1 93 62 5 AC-4 50.0 4.5 0.0 28.0 22.0
0.2 69 62 6 AC-4 60.0 4.5 0.0 34.8 5.2 0.2 62 38 7 AC-4 46.6 4.5
0.0 35.9 17.5 0.15 91 83 8 AC-4 55.0 4.5 0.0 24.0 21.0 0.15 56 58 9
AC-4 55.0 4.5 0.0 41.6 3.4 0.07 105 112 10 AC-4 55.0 4.5 0.0 41.6
3.4 0.23 72 69 11 AC-4 55.0 4.5 0.0 41.6 3.4 0.15 92 92 12 AC-4
55.0 4.5 0.0 41.6 3.4 0.15 90 83 13 AC-4 55.0 4.5 0.0 41.6 3.4 0.15
100 80 14 AC-4 55.0 4.5 0.0 41.6 3.4 0.15 96 68 15 AC-4 55.0 4.5
0.0 41.6 3.4 0.15 81 45 16 AC-1 55.0 4.5 0.0 41.6 3.4 0.15 89 51 17
AC-3 55.0 4.5 29.3 0.0 15.7 0.1 123 57 18 AC-3 55.0 4.5 0.0 41.5
3.5 0.1 111 89 19 AC-2 55.0 4.5 0.0 41.5 3.5 0.1 102 84 20 AC-6
55.0 6.0 15.2 20.0 9.8 0.1 133 53 21 AC-5 47.0 3.0 0.0 47.0 6.0
0.08 107 103 22 AC-5 55.0 3.0 0.0 41.0 4.0 0.08 91 68
[0045] In addition, as shown in Table 4, Examples 17 to 20 provided
good adhesion to a high density polyethylene (HDPE) panel, a very
difficult to adhere to, low surface energy substrate.
TABLE-US-00004 TABLE 4 Adhesion of Examples 17 to 20 to a HDPE
panel. Co- Weight percent (N/dm) polymer Acrylic SP- FORAL SYL.
90.degree. peel Ex. I.D. Copolymer 553 85LB A-25 Bisamide HDPE 17
AC-3 55.0 29.3 0.0 15.7 0.1 57 18 AC-3 55.0 0.0 41.5 3.5 0.1 61 19
AC-2 55.0 0.0 41.5 3.5 0.1 58 20 AC-6 55.0 15.2 20.0 9.8 0.1 51
[0046] Additional compositions based on adhesive copolymer AC-4 and
the associated test results are summarized in Table 5. The adhesive
samples were prepared as described above. All samples showed
excellent shear at 70.degree. C. using a stainless steel panel. The
shear test for each sample was terminated after 10,000 minutes with
no failure.
TABLE-US-00005 TABLE 5 Effects of varying the total amount of
tackifiers and the amount of crosslinker. Tackifiers wt. %) Acrylic
copolymer High Tg Low Tg wt. % FORAL ESTER wt. % 90.degree. peel
(N/dm) Ex. I.D. in adh. wt. % AA 85LB 3-E bisamide SS PP HDPE 23
AC-4 50.0 4.5 45.0 5.0 0.15 104 97 51 24 AC-4 55.0 4.5 41.5 3.5
0.10 97 100 65 25 AC-4 55.0 4.5 41.5 3.5 0.15 79 71 44 26 AC-4 55.0
4.5 41.5 3.5 0.20 71 71 37 27 AC-4 60.0 4.5 36.5 3.5 0.15 61 59
34
[0047] Examples 23, 25, and 27 illustrate the effect of decreasing
the amount of tackifiers relative to the amount of acrylic
copolymer in the adhesive. As the total amount of tackifier
decreases from 50 wt. % (EX-23), to 45 wt. % (EX-25), and further
to 40 wt. % (EX-27), the peel adhesion to both the high surface
energy stainless steel panel, and the low surface energy
polypropylene and HDPE panels decreased.
[0048] Examples 24, 25, and 26 illustrate the effect of increasing
the amount of crosslinker. While an increase in crosslinker level
decreased the adhesion to all substrates, the effect appears to be
greater for adhesion to the low surface energy substrates.
[0049] As summarized in Table 6A and 6B, the adhesive of Example 24
provides excellent adhesion to low surface energy substrates, good
adhesion to variety of other substrates, and adequate cohesive
strength as compared to a variety of commercial available
products.
TABLE-US-00006 TABLE 6A Comparison of Example 24 to commercially
available adhesives. 90.degree. Peel Thickness adhesion (N/dm) Ex.
Adhesive Source (microns) SS PP HDPE CE-5 300MP 3M Co. 51 59 26 18
CE-6 #350 3M Co. 51 72 26 25 CE-7 300LSE 3M Co. 51 83 41 39 CE-8
(a) #4965 Tesa 89 (.times.2) 87 52 38 EX-24 -- -- 51 97 100 65
TABLE-US-00007 TABLE 6B Comparison of Example 24 to commercially
available adhesives (continued). 90.degree. Peel adhesion Thickness
(N/dm) 70.degree. C. Shear (min.) Ex. Adhesive Source (microns)
PMMA PC ABS SS CE-5 300MP 3M Co. 51 56 54 52 66 CE-6 #350 3M Co. 51
76 42 69 7219 CE-7 300LSE 3M Co. 51 106 90 66 7088 CE-8 (a) #4965
TESA 89 (.times.2) 106 106 119 10000 EX-24 -- -- 51 102 100 90
10000 (a) Comparative Example C8 is a double coated tape having 89
microns of adhesive on both sides of a carrier.
[0050] Probe Testing. Probe tests of adhesive samples were
performed with a TA.XT PLUS TEXTURE ANALYZER (Stable Micro Systems
Ltd., UK) under ambient conditions. A cylindrical high-density
polyethylene probe with a diameter of 5.0 mm was brought into
contact with a 102 micron (4 mil) thick adhesive layer on a glass
slide under a contact force of 500 grams for 60 seconds. Then the
probe was pulled away with a constant velocity of 0.05 mm per
second until completely debonded. The force applied to the probe
was recorded as a function of the probe displacement distance. The
strength of the adhesive joint is given by the rupture energy,
which was calculated as an integration of the force against
displacement during the debonding process, i.e., the area under the
force-displacement curve. The results are summarized in Table
7.
TABLE-US-00008 TABLE 7 Probe Test results. Maximum Rupture wt. %
wt. % Maximum Displacement Energy I.D. tackifiers bisamide Force
(N) (mm) (N mm) EX-27 40 0.15 7.8 0.61 2.10 EX-25 45 0.15 9.1 0.70
3.01 EX-23 50 0.15 9.3 0.77 3.84 EX-24 45 0.10 8.1 1.13 5.03 EX-26
45 0.20 8.8 0.54 2.14
[0051] Compared to typical acrylic adhesives, in some embodiments,
the adhesives of the present disclosure exhibit strain-hardening
behavior, i.e., the tensile force needed to separate the adhesive
joint goes up as the strain on the adhesive increases. As a result,
the adhesive strength (e.g., the area under the force-displacement
curve) is significantly greater. Also, as the total combined amount
of the high Tg and low Tg tackifiers increases from 40 wt. %
(EX-27), to 45 wt. % (EX-25), and further to 50 wt. % (EX-23), both
the maximum force and the maximum displacement at the point of
final joint rupture increase. Thus, the area under the
force-displacement curve is increased, indicating a stronger
adhesive joint.
[0052] Adhesive samples were prepared according to the compositions
set forth in Table 8 using the method described above. All samples
contained 0.10 weight percent bisamide crosslinker based on the
weight of the acrylic copolymer. As shown in Table 8, increasing
the amount of high Tg tackifier from 0 to 40% by weight led to
increased adhesion to stainless steel and polypropylene (CE-9 to
CE-11). However, further increasing the amount of high Tg tackifier
to 50 wt. % and 60 wt. % resulted in a decrease in both the
adhesion to the low surface energy polypropylene substrate and the
shear strength (CE-12 and CE-13). Significantly better adhesion to
polypropylene was achieved using a combination of high and low Tg
tackifiers (Examples EX-28 and EX-29) rather than a single high Tg
tackifier at comparable or even higher total tackifier loadings
(CE-12 and CE-13). Thus, merely increasing the amount of a single
high Tg tackifier in an adhesive is not as effective as combining a
high Tg tackifier and a low Tg tackifier to achieve adhesives
according to the present disclosure.
TABLE-US-00009 TABLE 8 Effects of including a low Tg tackifier.
Weight % in the adhesive 90.degree. peel 70.degree. C. Acrylic
FORAL ES2520 (N/dm) Shear (min.) Tg (K) Ex. polymer 85LB high Tg
low Tg SS PP SS Fox (c) DSC (d) CE-9 100 0 0 36 14 10000+ 224 224
CE-10 70 30 0 67 43 10000+ 245 242 CE-11 60 40 0 91 62 10000+ 253
247 CE-12 50 50 0 131 52 10000+/ (b) 261 253 CE-13 40 60 0 74 46
300 270 261 EX-28 50 45 5 122 106 10000+ 259 252 EX-29 50 40 10 117
113 10000+ 256 250 (b) Two samples held for 10,000+ minutes, one
sample failed at 4312 minutes. (c) Glass transition temperature as
calculated using the Fox Equation. (d) Glass transition temperature
as measured by differential scanning calorimetry.
[0053] The effect of filler concentration was evaluated by adding
various amounts of fumed silica (AEROSIL R972V obtained from
Degussa Corp., "R972V") to an adhesive system comprising an acrylic
copolymer (AC-4), a high Tg tackifier (FORAL 85LB), a low Tg
tackifier (ES2520), and 0.1 wt. % of bisamide crosslinker. The
amount of filler is reported in parts by weight per hundred parts
of adhesive (i.e., per 100 parts of combined acrylic copolymer and
total tackifier). The adhesive samples were prepared according to
the method described above, except the samples were coated on the
HOSTAPHAN W270 with opaque polyester backing. The 180.degree. peel
from polypropylene and the 70.degree. C. shear from stainless steel
were tested and the results are reported in Table 9. "Cohesive"
indicates cohesive failure of the adhesive layer. "Clean" indicate
clean removal of the adhesive from the panel.
TABLE-US-00010 TABLE 9 Effect of filler loading on adhesive
performance. pph 180.degree. 70.degree. C. Weight % in the adhesive
ad- peel from PP Shear Acrylic high Tg low Tg hesive failure SS Ex.
polymer tackifier tackifier R972V N/dm mode (min.) EX-30 52.5 42
5.5 0.0 123 Co- 300 hesive EX-31 52.5 42 5.5 2.5 91 Clean 10000+
EX-32 52.5 42 5.5 5.0 86 Clean 10000+
[0054] Additional examples were prepared to compare the performance
of adhesives comprising both a high Tg and a low Tg tackifier, to
similar adhesives comprising a high Tg tackifier and a plasticizer.
The adhesives were prepared as described above except the adhesives
were coated on a 51 micron (2 mil) white opaque polyester film
backing (HOSTAPHAN W270 available from Mitsubishi Polyester Film,
Inc.). Under the heading for compatibility (Compat.), "Good"
indicates a clear adhesive film, "Fair" indicates a slightly haze
film, and "Poor" indicates a haze film.
TABLE-US-00011 TABLE 10 Tg tackifier-containing adhesives compared
to plasticizer-containing adhesives. Weight % in the adhesive
180.degree. FORAL peel Acrylic 85LB low Low Tg
tackifier/plasticizer (24 hr.) Ex. polymer high Tg Tg material type
I.D. Comp. PP (N/dm) EX-33 52.5 40.0 7.5 tackifier SYL. A-25 Fair
104 EX-34 52.5 40.0 7.5 tackifier ES 2520 Good 121 EX-35 52.5 40.0
7.5 tackifier ESTER 3E Good 116 CE-14 52.5 40.0 7.5 plasticizer
PYCAL 94 Good 84 CE-15 52.5 40.0 7.5 plasticizer G1000 Poor 76
[0055] Generally, adhesives according to the present disclosure may
be used in any typical adhesive applications. In some embodiments,
the adhesive may be used as a free (i.e., unsupported) adhesive
film. In some embodiments, adhesive articles such as tapes may be
useful. In some embodiments, the adhesive may be bonded to a
substrate, e.g., a paper, a polymeric film, a scrim, a foil, and
the like. In some embodiments, the adhesive may be directly bonded
to the substrate. In some embodiments, the adhesive may be
indirectly bonded to the substrate, i.e., there are one or more
intervening layers (e.g., primer layers) between the adhesive and
the substrate.
[0056] In some embodiments, the adhesive or adhesive articles may
be used to bond two substrates together. For example, a layer of
adhesive may be used to bond a first substrate to a second
substrate. In some embodiments, at least one of the substrates is a
low surface energy substrate, i.e., a substrate having a surface
energy of less than 40 millinewtons per meter (mN/m), e.g., less
than 35 mN/m. Exemplary low surface energy materials include
polyolefins such as polypropylene and polyethylene (e.g., high
density polyethylene).
[0057] Exemplary adhesive article 10 according to some embodiments
of the present disclosure is illustrated in FIG. 1. Adhesive
article 10 comprises adhesive 12 bonded to first substrate 14.
Adhesive 12 is indirectly bonded to first substrate 14, as optional
primer layer 16 is interposed between adhesive 12 and first
substrate 14. As shown in FIG. 1, adhesive article 10 is bonded to
second substrate 20, which may be a low surface energy
substrate.
[0058] Various modifications and alterations of this invention will
become apparent to those skilled in the art without departing from
the scope and spirit of this invention.
* * * * *