WO2022141146A1

WO2022141146A1 - Cured silicone adhesive composition

Info

Publication number: WO2022141146A1
Application number: PCT/CN2020/141207
Authority: WO
Inventors: Christopher B. Walker; Chao Yang
Original assignee: 3M Innovative Properties Company; Chao Yang
Priority date: 2020-12-30
Filing date: 2020-12-30
Publication date: 2022-07-07
Also published as: TW202242028A

Abstract

The present invention provides a cured silicone adhesive composition, the cured silicone adhesive composition, comprising a chemically cross-linked reaction product of the following reaction components: an optional vinylfunctional siloxane having a vinyl functionality of 2 or more and diphenylsiloxane units; a siloxane gum comprising diphenyl siloxane groups, and vinylalkyl siloxane groups; an effective amount of a tackifier; wherein the total weight percentage of diphenylsiloxane units is 6%to 11%, according to theformula-Si (Ph) ₂-O-, based on the total weight of the cured silicone adhesive composition, the cured silicone adhesive composition has a tan delta of at most 0.9 for a temperature equal to 200℃, and the cured silicone adhesive composition has a tan delta of at least 0.27 in a temperature range from 25℃ to 200℃, as measured by a rheo logical curve. Dampmg films comprising sueh cured silicone adhesive are provided. Microspeaker diaphragm materials comprising such damping films are also provided. Manufacturing methods of damping filins are also provided.

Description

CURED SILICONE ADHESIVE COMPOSITION

TECHNICAL FIELD

This disclosure relates to the technical field of cured adhesives, and particularly, to cured silicone adhesive for use as damping adhesive layer in sheet materials, such as may be converted into microspeaker diaphragms.

BACKGROUND

Microspeakers are increasingly common in small electronics such as cell phones, tablets, earbuds, headphones and laptop computers. Microspeakers diaphragms are ideally light weight and very rigid, so as to exhibit pure pistonic motion, and also well damped, to suppress undriven motion or resonances that result in distorted reproduction of sound. In some cases, diaphragm materials are multi-layer membranes comprising at least a damping layer.

The damping layer may also function as an adhesive binding other layers together. The majority of microspeaker diaphragm damping adhesives are employed in 3 layer laminate constructions in which the adhesive is deployed between 2 layers of PEEK, an expensive thermoplastic with Tg of～143℃. As the PEEK is typically very thin (5-9 microns) , it is challenging to handle it as a web in a traditional coating line. It is even more difficult to cure an adhesive at elevated temperatures on PEEK if the temperatures approach or surpass the Tg of PEEK.

As peroxide cure of silicones with benozyl peroxide requires temperatures of 150℃ or higher, coating and curing it on PEEK is excessively challenging as the PEEK shrinks in the curing ovens, changing the dimensions of the coated adhesive. Consequently, constructing PEEK laminates with peroxide cured silicones require coating the adhesive on an expensive fluorosilicone treated liner, which must be subsequently removed and the PEEK film laminated to the adhesive. If 2 liners are used, the process must be repeated twice. Liner removal and PEEK lamination adds production steps, lowers yield, and increases cost relative to coating directly on PEEK.

It would be desirable to have a silicone adhesive that could provide the properties of high temperature damping at key microspeaker frequencies while maintaining high shear performance at elevated temperatures. And the cured silicone adhesive has low Tg (i.e., lower than 0 ℃) without the use of high temperatures (i.e., greater than 150 ℃) and long time curing.

SUMMARY

In view of the technical problems above, an object of the present disclosure is to provide a cured silicone adhesive composition, comprising a chemically cross-linked reaction product of the following reaction components: an optional vinyl functional siloxane having a vinyl functionality of 2 or more and diphenylsiloxane units; a siloxane gum comprising diphenyl siloxane groups, and vinylalkyl siloxane groups; an effective amount of a tackifier; wherein the total weight percentage of diphenylsiloxane units is 6%to 11%, according to the formula -Si (Ph) ₂-O-, based on the total weight of the cured silicone adhesive composition, the cured silicone adhesive composition has a tan delta of at most 0.9 for a temperature equal to 200℃, and the cured silicone adhesive composition has a tan delta of at least 0.27 in a temperature range from 25℃ to 200℃, as measured by a rheological curve.

In another aspect, the present disclosure provides a damping film comprising a cured silicone adhesive composition according to the present disclosure.

In another aspect, the present disclosure provides a microspeaker diaphragm comprising a damping layer, wherein the damping layer is a damping film according to the present disclosure.

In another aspect, the present disclosure provides a method of manufacturing a damping film used for microspeaker, the damping film comprising a cured silicone adhesive composition and an optional stiff layer, the method comprises a chemical crosslinking treatment to a reaction product of the following reaction components by radiation: an optional vinyl functional siloxane having a vinyl functionality of 2 or more and diphenylsiloxane units; a siloxane gum comprising diphenyl siloxane groups, and vinylalkyl siloxane groups; an effective amount of a tackifier; wherein the total weight percentage of diphenylsiloxane units is 6%to 11%, according to the formula -Si (Ph) ₂-O-, based on the total weight of the cured silicone adhesive composition, the cured silicone adhesive composition has a tan delta of at most 0.9 for a temperature equal to 200℃, and the cured silicone adhesive composition has a tan delta of at least 0.27 in a temperature range from 25℃ to 200℃, as measured by a rheological curve.

In some embodiments of the method of the present disclosure, the cured silicone adhesive composition has a tan delta of at least 0.35 in a temperature range from 25℃ to 200℃, as measured by a rheological curve.

In some embodiments of the method of the present disclosure, the diaphragm comprises two or more stiff layers and at least one damping layer, where the damping layer is a damping film according to the present disclosure.

In some embodiments, the chemical cross-linking is accomplished by radiation in the absence of any free radical initiators or photoinitiators and in the absence of silicone hydride functional crosslinkers and the precious metal catalysts known to promote addition cure crosslinking via reaction of alkenyl groups on one polymer chain with silicone hydride groups on another polymer chain.

Additional embodiments of the microspeaker diaphragm materials of the present disclosure are descrived below under “Selected Embodiments. ”

Compared with the prior art, the present invention has the following beneficial effects:

1) The silicone adhesive damping material has high temperature damping performance while maintaining high temperature shear performance.

2) The silicone adhesive can be cured at temperature lower than 146℃, and it can be easily coated and cured directly on stiff layer to form a lamination structure.

3) The curable silicone adhesive does not require the use of expensive precious metal catalysts, high temperature or long time curing.

The preceding 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

The disclosure may be more completely understood in consideration of the following detailed description of various embodiments of the disclosure in connection with the accompanying figures, in which:

FIG. 1 is a graph presenting dynamic mechanical analysis data measured for one embodiment (that is, Example 1) of the present disclosure; and

FIG. 2 is the 25℃ master curve of Example 1.

DETAILED DESCRIPTION AND ILLUSTRATIVE EMBODIMENTS

The present invention will be further described in detail below in conjunction with the embodiments. It will be appreciated that other embodiments are considered, and can be practiced without departing from the scope and spirit of the present invention. Therefore, the following detailed description is non-limiting

Unless otherwise specified, all numbers used in this Description and the Claims representing the characteristic sizes and quantities and physical properties should be understood as being modified by the term “approximately” under any and all circumstances. Therefore, unless stated on the contrary, parameters in numerical values listed in the above description and in the attached claims are all approximate values, and those of skill in the art are capable of seeking to obtain desired properties by taking advantage of contents of the teachings disclosed herein, and changing these approximate values appropriately. The use of a numeric value range represented by endpoints includes all numbers within such range and any range within such range, e.g., 1 to 5 includes 1, 1.1, 1.3, 1.5, 2, 2.75, 3, 3.80, 4 and 5 etc.

In this application:

As used in this speficication and the appended claims, the singular forms “a” , “an” , and “the” encompass emobodiments having plural referents, unless the content clearly dicates otherwise.

As used herein, “have” , “having” , “include” , “including” , “comprise” , “comprising” or the like are used in their open ended sense, and generally mean “including, but not limited to” . It will be understood that the terms “consisting of” and “consisting essentially of” are subsumed in the term “comprising” , and the like.

As used herein, the terms “cure” and “curable” refer to joining polymer chains together by covalent chemical bonds, usually via crosslinking molecules or groups, to form a network polymer. Therefore, in this disclosure the terms “cured” and “crosslinked” may be used interchangeably. A cured or crosslinked polymer is generally characterized by insolubility, but it may be swellable in the presence of an appropriate solvent. Polymers that are not crosslinked will soften and flow at high temperatures, where as those that are crosslinked will not flow at higher temperatures.

As used herein, polysiloxanes are polymers comprising repeating repeating Si -O -units in which the number of repeating units may be tens to hundreds to millions of repeat units. As silicone is tetravalent, the polysiloxanes also include substituents on the silicone atom. These substituents may be the same or different and often include aliphatic or aromatic groups bonded to the silicone atom. The polysiloxane may include copolymers in which some of the repeats units are - (R ₁R ₂ Si-O ) -other units are - (R ₃R ₄ Si-O ) -and other units are - (R ₅R ₆ Si-O) -where the R groups are hydrogen, aliphatic, alkenyl, or aromatic groups. In many cases the polysiloxanes are terminated with R ₇Si-O groups. If there are different types of repeat units present, the polysiloxane is considered a copolymer.

As used herein, the term “siloxane” and “silicone” are interchangeable.

As used herein, the term “aliphatic” refers to C1-C40, suitably C1-C30, straight or branched chain alkenyl, alkyl, or alkynyl which may or may not be interrupted or substituted by one or more heteroatoms such as O, N, or S.

As used herein, the term “aromatic” refers to C3-C40, suitably C3-C30, aromatic groups including both carbocyclic aromatic groups as well as heterocyclic aromatic groups containing one or more of the heteroatoms, O, N, or S, and fused ring systems containing one or more of these aromatic groups fused together.

As used herein, the term “alkyl” refers to a monovalent group that is a radical of an alkane and includes straight-chain, branched, cyclic, and bicyclic alkyl groups, and combinations thereof, including substituted alkyl groups. Unless otherwise indicated, the alkyl groups typically contain from 1 to 30 carbon atoms. In some embodiments, the alkyl groups contain 1 to 20 carbon atoms, 1 to 10 carbon atoms, 1 to 6 carbon atoms, 1 to 4 carbon atoms, or 1 to 3 carbon atoms. Examples of “alkyl” groups include, but are not limited to, methyl, ethyl, n-propyl, n-butyl, n-pentyl, isobutyl, t-butyl, isopropyl, n-octyl, n-heptyl, ethylhexyl, cyclopentyl, cyclohexyl, cycloheptyl, adamantyl, norbornyl, and the like.

As used herein, the term “vinylalkyl silicone group” refers to a group with a silicone atom in the middle of the polysiloxane chain having one vinyl group and one alkyl group and 2 oxygen atoms in turn bonded to two more silicone atoms, e.g. Si -O -Si -O -Si, with the vinyl alkyl substituted silicone as the midlle of this group and the repeating Si-O units create a polysilooxane chain hundreds if not thousand or tens of thousand units long.

As used herein, the term “alkenyl” refers to a group which is characterized by the presence of a carbon carbon double bond, also referred to as unsaturated carbons. Vinyl groups are a very significant type of alkenyl group that participates in radical crosslinking reactions. The carbon carbon double bond may be directly attached to the silicone atom or there may be saturated carbon atoms (e.g. -CH ₂-CH ₂-groups between the silicone atom and the alkenyl group. If the carbon-carbon double bond consists of a -CH=CH ₂ group directly bonded to the silicone atom (e.g. Si-CH=CH ₂) , this also referred to as a vinyl group. Unless otherwise indicated, the alkylene group typically has 1 to 30 carbon atoms. In some embodiments, the alkylene group has 1 to 20 carbon atoms, 1 to 10 carbon atoms, 1 to 6 carbon atoms, or 1 to 4 carbon atoms.

As used herein, the term “aryl” refers to a monovalent group that is aromatic and, optionally, carbocyclic. The aryl has at least one aromatic ring. Any additional rings can be unsaturated, partially saturated, saturated, or aromatic. Optionally, the aromatic ring can have one or more additional carbocyclic rings that are fused to the aromatic ring. Unless otherwise indicated, the aryl groups typically contain from 6 to 30 carbon atoms. In some embodiments, the aryl groups contain 6 to 20, 6 to 18, 6 to 16, 6 to 12, or 6 to 10 carbon atoms. Examples of an aryl group include phenyl, naphthyl, biphenyl, phenanthryl, and anthracyl.

The present invention provides a cured silicone adhesive composition, comprising a chemically cross-linked reaction product of the following reaction components: an optional vinyl functional siloxane having a vinyl functionality of 2 or more and diphenylsiloxane units; a siloxane gum comprising diphenyl siloxane groups, and vinylalkyl siloxane groups; an effective amount of a tackifier; wherein the total weight percentages of diphenylsiloxane units being 6%to 11%, according to the formula -Si (Ph) ₂-O-, based on the total weight of the cured silicone adhesive composition , the cured silicone adhesive composition has a tan delta of at most 0.9 for a temperature equal to 200℃, and the cured silicone adhesive composition has a tan delta of at least 0.27 in a temperature range from 25℃ to 200℃, as measured by a rheological curve.

Vinyl functional silicones

Typically, the vinyl functional silicones, suitable for present disclosure, contain 2 or more vinyl groups per polymer chain. When the number of either functional groups is equal to or greater than 2, the system crosslinks -what were previously different polymer chains are now covalently attached. With sufficient crosslinking, all of the polymer chains are connected. Extremely high molecular weights are achieved and adhesive properties such as high temperature shear performance are greatly enhanced.

In some embodiments, when the vinyl functional silicone having a Mw of equal to or more than 300,000 or 400,000, or 500,000, or 600,000 or 700,000, or 800,000 is used, a good high temperature shear result and high temperature damping result will be achieved. Moreover, the amount of the vinyl functional silicones in the reaction components of the cured silicone adhesive composition is from as at least 9 wt%, at least 15 wt%, at least 20 wt%, at least 25 wt%, at least 30 wt%, at least 35 wt%, or at least 40 wt%and up to 70 wt%, up to 65 wt%, up to 60 wt%, up to 55 wt%, or up to 50 wt%.

In some embodiments, when the vinyl functional silicone includes a small molecular weight vinyl functional silicone having a Mw of equal to or less than 60,000, or 55,000, or 50,000, the amount of small molecular weight vinyl functional silicone is from at most 1 wt%, or at most 2 wt%, or at most 3 wt%, or at most 4 wt%, or at most 5 wt%, or at most 6 wt%.

Preferably, the vinyl functional silicones have a functionality (Vinyl group) of 2 or more. The method for determining the functionality comprises: determining the number average molecular weight (Mn) by using gel permeation chromatography (GPC) , and calculating the functionality by combining the Mn determined by GPC and the total number of functional groups determined by nuclear magnetic resonance spectroscopy (NMR) . When the functionality of the vinyl functional silicone is in the above range, the reactivity of the vinyl functional silicones can be controlled.

When the vinyl functional silicone having a functionality of less than 2 is used, an insufficient crosslinked network leads to poor high temperature resistance.

Moreover, the amount of the vinyl functional silicones in the reaction components of the cured silicone adhesive composition is from as at least 9 wt%, at least 15 wt%, at least 20 wt%, at least 25 wt%, at least 30 wt%, at least 35 wt%, or at least 40 wt%and up to 70 wt%, up to 65 wt%, up to 60 wt%, up to 55 wt%, or up to 50 wt%. In some embodiments, the amount of the vinyl functional silicones is in a range of 9 to 70 wt%, and preferably from 9 to 20 wt%.

According to some embodiments of the present invention, the cured silicone adhesive compositions comprise a vinyl functional silicone have diphenylsiloxane units as an essential component. Without diphenylsiloxane units, the vinyl functional silicone can’t react well with the silicone gum to make a good PSA, e.g. blends of vinyl terminated polydimethylsiloxane (155,000 molecular weight) , vinyl-alkyl-diphenyl gums and MQ tackifier are often immiscible in proportions needed to get to a Tg of-20 to -30℃.

In some embodiments, the vinyl functional silicones have diphenylsiloxane units. The diphenylsiloxane units could be provided by another source, such as siloxane gum. That is, an appropriate amount of diphenylsiloxane units in both silicon gum and vinyl functional silicone is preferred.

In some embodiments, the vinyl functional silicones have diphenylsiloxane units. The diphenylsiloxane units could be provided by another source, such as siloxane gum. The diphenylsiloxane units may be present in the cured silicone adhesive composition, in a formula -Si (Ph) ₂-O-, in a total amount of between 6 wt%and 11 wt%, or between 6 wt%and 10 wt %, or between 7 wt%and 9.5 wt %, based on the total weight of the cured composition.

In some preferred embodiments, the vinyl functional silicones include dimethyl siloxane-co-diphenyl siloxane-co-vinylmethyl siloxane. The dimethyl siloxane-co-diphenyl siloxane-co-vinylmethyl siloxane has 10.0 -16.0 mass percentages of diphenyl groups, 75-90 mass percentages of dimethyl groups , 0.02 -0.25 mass percentages of vinylmethyl groups and vinyl equivalent weights of 30,000 -100,000 g/eq. Examples of vinyl functional siloxanes includes VGP-061, available from Gelest:

In some preferred embodiments, the vinyl functional silicones include vinyl terminated polydimethylsiloxane-co-diphenyl siloxane. Example of vinyl functional siloxanes includes divinyl terminated polydimethylsiloxane-co-diphenyl siloxane with 10-40 mass percentages of diphenyl groups, 60-90 mass percentages of dimethyl groups and vinyl equivalent weights of 3,000-25,000 g/eq. Examples of vinyl functional siloxanes includes PDV0541 available from Gelest, and CAS 68951-96-2 (e.g. Gelest PDV-1631) shown below:

It may be possible to add a small amount (e.g. less than 10 wt. %or less than 6 wt. %based on the total weight of vinyl functional silicone) of the vinyl terminated polydimethylsiloxane to above mentioned vinyl functional siloxane with diphenyl-co-dimethyl group and still be miscible. Examples of vinyl terminated siloxanes are those sold by Gelest, Inc of Morrisville, PA and have vinyl groups on the end of the chain (e.g. Gelest DMS-V42 CAS 68083-19-2) as shown here:

Vinyl functionality may also be located on the interior ofpolysiloxanes. It may be possible to add this type of polysiloxanes to the vinyl functional siloxane with diphenyl-co-dimethyl group and still be miscible. An example is the structure as shown below representing CAS 67762-94-1 (e.g. Gelest VDT-163) :

Silicone gum

Silicone gums of this disclosure are vinyl functional silicone gum having vinyl functionality of 2. In some preferred embodiments, the vinyl functional silicone gums comprise diphenyl siloxane groups, and vinyl methyl siloxane groups; wherein the vinyl functionality is located on the gum and is not on the tackifier. Silicone gums includes dimethyl-co diphenyl-co vinyl methyl gum, and the vinyl groups are not on the end of the gum.

In some embodiments, a suitable silicone gum comprises diphenyl siloxane groups (D _Ph2) , dimethyl siloxane groups (D ₂) and vinylmethyl siloxane groups (D _vi) , with the following mass percentages ranges: D _Ph2 of 11-17; D ₂ of 82-89; D _vi of 0.03-0.09 and vinyl equivalent weight of 100,000 to 200,000 g/eq. An example is the gum present as part of the adhesive sold by Shin Etsu as KCT009AC, the other part of the adhesive is the MQ tackifier.

In some embodiment, a suitable silicone gum comprises vinyl methyl siloxane-co-dimethyl siloxane-co-diphenyl siloxane, which has 11-17 mass percentages of diphenyl siloxane groups, 82-89 mass percentages of dimethyl siloxane groups, 0.03-0.09 mass percentages of vinylmethyl siloxane groups and vinyl equivalent weights of 100,000 to 200,000 g/eq.

In some embodiments, a suitable silicone gum comprises diphenyl siloxane groups (D _Ph2) , dimethyl siloxane groups (D ₂) and vinylmethyl siloxane groups (D _vi) , with the following mass percentages ranges: D _Ph2 of 11-17; D ₂ of 82-89; D _vi of 0.02-0.2 and vinyl equivalent weight of 50,000 to 200,000 g/eq. An example is the gum present as part of the adhesive sold by Shin Etsu as KCT009AC, the other part of the adhesive is the MQ tackifier.

In some embodiments, an examples of silicone gum includes VGP-061, available from Gelest.

Tackifiers

In some embodiments, the cured silicone adhesive compositions of the present disclosure may optionally include one or more tackifiers.

The tackifiers for cured silicone adhesive compositions are invariably MQ resins. These materials possess “Q” groups with Si bonded to 4 oxygen atoms and “M” groups with Si bonded to 1 oxygen atom and 3 carbon atoms. The 3 carbons are usually methyl groups. Q4 groups are silicone atoms bonded to 4 oxygen atoms and each of the 4 oxygen atoms is in turn attached to another silicone atom. Q3 groups are silicone atoms bonded to 4 oxygen atoms and 3 of the oxygen atoms are bonded to another silicone atom. Typically, the 4th oxygen atom is bonded to a hydrogen atom. There are M and Q groups in all silicone adhesive tackifiers of disclosure. MQ resins are available from Dow (Dowsil 2-7066) and Momentive (SR 545) . Siltech offers MQ resin where some of the “M” groups are replaced with vinyl functionality, e.g. (CH ₂=CH) Si (CH ₃) ₂ -O -under the brand Silmer; two examples are Silmer VQ20 and VQXYL. SiVance offers 100%solids MQ as MQOH7.

Moreover, the amount of the tackifiers in the cured silicone adhesive composition is from as at least 30 wt%, at least 35 wt%, at least 45 wt%, and up to 70 wt%, up to 65 wt%, up to 60 wt%, up to 55 wt%, or up to 50 wt%. In some embodiments, the amount of the tackifier is in a range of 30 to 70 wt%, and preferably from 40 to 60 wt%.

Radiation crosslinking

E-beam crosslinking can be carried out by any suitable method. Commercially available electron beam generating equipment are available, including those available from Energy Sciences, Inc. (Wilmington, MA) . Generally, a support film or liner runs through an inert chamber, typically a nitrogen atmosphere. In some embodiments, a sample of uncured material with a liner on both sides is treated. In some embodiments, a sample of the uncured material may be applied to one liner, with no liner on the opposite surface ( “open face” ) . In some embodiments a sample of uncured material on a substrate may be subjected to e-beam irradiation through the substrate. In some embodiments a laminate of substrate -uncured adhesive -substrate may be e-beam treated from oner both sides to cure and crosslink the adhesive. In some preferred laminates, the substrate layer is PEEK. The material may be exposed to E-beam irradiation from one side through the release liner. In some embodiments, no catalysts or initiators are employed, and thus such compositions are “substantially free” of any catalysts or initiators. As used herein, a composition is “substantially free of catalysts and initiators” if the composition does not include an “effective amount” of a catalyst or initiator. As is well understood, an “effective amount” of a catalyst or initiator depends on a variety of factors including the type of catalyst or initiator, the composition of the curable material, and the curing method (e.g., thermal cure, UV-cure, and the like) . some embodiments, a particular catalyst or initiator is not present at an “effective amount” if the amount of catalyst or initiator does not reduce the cure time of the composition by at least 10%relative to the cure time for same composition at the same 20 curing conditions, absent that catalyst or initiator. In some embodiments, the e-beam exposure is limited to between 1.2 and 4.5 Mrad of e-beam radiation at a voltage of greater than 100 kV or more typically greater than 150 kV. Additional embodiments may be limited to the film thicknesses, compositions, conditions and/or exposures recited in the Selected Embodiments below.

Rheological curve

The “rheological curve” according to the present invention is measured by using an Ares DHR-2 Rheometer produced by the TA Instruments, New Castle Delaware, USA, in which an 8 millimeter parallel plate clamp is used to hold a chemically cross-linked silicone sample have a thickness of less than or equal to 1 mm, and when the heating rate is 3℃/min, the testing frequency is 1 Hz, and the strain is 2 to 5%, rheological measurement is performed at different temperature points to obtain the storage modulus G’ and the loss modulus G”, and further according to the following formula, the loss factor value (that is, the damping value) tanδ is calculated from the storage modulus G’ and the loss modulus G”:

tan δ=G” /G’

According to the above formula, when the silicone adhesive composition is chemically cross-linked and when the chemically cross-linked silicone adhesive composition has a loss factor (tan delta) of at most 0.9 for a temperature equal to 200℃, as measured by a rheological curve, it may be indicated that the silicone adhesive composition has good thermal stability (that is, high temperature damping property) .

Cured silicone adhesive

In some embodiments, the cured silicone adhesive compositions, may have a glass transition temperature that ranges from -12℃ to -31℃.

When the glass transition temperature of cured silicone adhesive composition is too high (i.e. greater than -12℃ in 1 Hz rheology) , the frequency of maximum damping in a 25℃ master curve is too low (＜100 Hz) . The glass transition temperature range of the cured silicone adhesive composition needs to meet the requirements (i.e., in the range of from -14 ℃ to -31℃) . In some embodiments, cured silicone adhesive composition having a glass transition temperature of at least -12 ℃, at least -14 ℃, and at least -16 ℃. This demonstrates that when the cured silicone adhesive composition has a glass transition temperature ranging from -12 ℃ to -31 ℃, , the adhesive film has a good overall performance in terms of maximizing damping of frequencies of interest (typically 100-1000 Hz) in the handheld device microspeakers.

¹H work is done on a Bruker Avance III 500 MHz NMR spectrometer. ²⁹Si work is done on a JEOL ECZ600R 600 MHz NMR spectrometer. Portions of the submitted samples were analyzed as solutions of unknown concentration in deuterated tetrahydrofuran (THF) . One dimensional (1D) proton can be collected in standard tubes in the standard way. One of the residual proto-solvent resonances was used as a secondary chemical shift reference in the proton dimension (δ=1.73 ppm) . All the NMR data were collected with the samples held at 25℃. In the absence of MQ resin, the amount of D _ph2 can be determined from the proton spectrum, even in the presence of toluene. The integrals of the NMR signals are proportional to the number of moles of those protons. Dividing the integrals of different groups by the number of protons in resonance results in the number of moles of that moiety. By dividing the D _ph2 integral by 10 and the D ₂ integral by 6 will result in the relative moles of D _ph2 and D ₂. The presence of toluene does not obscure this quantification. The presence of MQ resins in the proton spectrum is insufficient for a full quantification. In this case, the sample is dissolved in deuterated THF and put into a 10mm FEP NMR tube to avoid background signal from the glass N. MR tubes. The data is collected on a JEOL 600 MHz instrument on a Silicone free probe to avoid background signal. A recycle delay of 60 seconds is used to collect a ²⁹Si spectrum. In these cases, each moiety has only a single ²⁹Si so integration of the different regions results in the direct molar ratio of the different groups. Ifa solvent is present, the two types of spectra ¹H and ²⁹Si are used together using one or more resonance as a cross-integration standard.

In another aspect, the present disclosure provides a damping film comprising a cured silicone adhesive composition according to any one of the previous embodiments.

In some embodiments, the damping film, may have a shear adhesion strength at 70℃ with 1000 gram Weight, on stainless steel, of 1,000 minutes or more, or preferred of 10,000 minutes or more, or preferred of 20,000 minutes or more.

In some embodiments, the damping film may have a shear adhesion strength at 70℃ with 500 gram Weight, on stainless steel, of 1,000 minutes or more, or preferred of 10,000 minutes or more, or preferred of 20,000 minutes or more.

In some embodiments, the damping film may have a tan delta of at least 0.27 in a temperature range from 25℃ to 200℃.

In some embodiments, the damping film may have a tan delta of at least 0.35 in a temperature range from 25℃ to 200℃.

In some embodiments, the method for chemically crosslinking the silicone adhesive composition is not particularly limited and the conventional physical and chemical methods can be used, such as electron beam radiation crosslinking, microwave radiation crosslinking, ultraviolet radiation crosslinking, and the like. Preferably, the silicone adhesive composition is cured by radiation, especially by radiating electron beam. The electron beam radiation comprises radiating the cured silicone adhesive using an electron beam having electron beam energy of 100 to 300 KV for an electron beam dose of 2.5 to 4.5 Mrad. E-beam exposure creates radicals on the siloxane polymer and these radicals can crosslink the vinyl siloxane or vinyl gum by reacting with the carbon-carbon double bonds. Lower electron beam dose is preferred to avoid overheating substrates or reaction of the adhesive with the liner. In some embodiments, the lower limit of electron beam dose is 1.0 Mrad, 1.2 Mrad, 1.4 Mrad or 1.8 Mrad; the upper limit of electron beam dose is 3.0 Mrad, or 3.5 Mrad, or 4.0 Mrad or 4.5 Mrad.

In another aspect, the present disclosure provides a diaphragm for a microspeaker comprises a damping illin, wherein the damping film comprising at least a damping illin according to any one of the previous embodiments.

In some embodiments, the diaphragm for a microspeaker having multilayer laminate constructions, and the damping film further comprising at least a stiff layer.

Any suitable stiff layers may be used in embodiments of the present disclosure. In some embodiments, stiff layers comprise high temperature engineering thermoplastics. In some embodiments, stiff layers comprise materials selected from the group consisting of: polyethylene terephthalate (PET) , polycarbonate (PC) , polybutylene terephthalate (PBT) , polyethylene naphthalate (PEN) , polyetheretherketone (PEEK) , polyetherketone (PEK) , polyetherimide (PEI) , polyimide (PI) , polyarylate (PAR) , polyphenylene sulfide (PPS) , polyphenylsulfone (PPSU) , polysulfone (PSU) , polyethersulfone (PES) , polyurethane (PU) , and a liquid crystal polymer (LCP) .

In some embodiments, stiff layers comprise polyether ether ketone (PEEK) . In some preferred embodiments, stiff layers comprise two PEEK stiff layers. As the PEEK is typically very thin (5-9 micron) , it is challenging to handle as a web in a traditional coating line. It is even more difficult to cure an adhesive at elevated temperatures on PEEK if the temperatures approach or surpass the Tg of PEEK. As peroxide cure of silicones with benzoyl peroxide requires temperatures of 150℃ or higher, coating and curing on PEEK is excessively challenging as the PEEK shrinks in the curing ovens, changing the dimensions of the coated adhesive. The cured silicone adhesive composition of current disclosure can be easily coated and cured directly on PEEK stiff layer to form a lamination structure.

Hereinafter, the present invention is described in detail by way of embodiments. It is to be understood that the description and embodiments are intended to be illustrating, rather than limiting the present invention. The scope of the present invention is defined by the appended claims.

Examples

Unless otherwise noted, all reagents were obtained or are available from Aldrich Chemical Co., Milwaukee, WI, or may be synthesized by known methods.

In the present invention, unless otherwise indicated, the used reagents are all commercially available and are used directly without further purification. Further, the “%” mentioned is “wt%” , and the “parts” mentioned are “parts by weight. ”

Test Methods

The various cured silicone adhesives prepared in the exampless and comparative examples are tested for the adhesion property (Shear Adhesion Strength at 70℃) and Dynamic Mechanical Analysis according to the specific methods listed below.

Shear Adhesion Strength at 70 ℃ with 1000 gram Weight

Shear adhesion strength at 70℃ was measured according to ASTM D3654/D 3654M-06: “Standard Test Methods for Shear Adhesion of Pressure Sensitive Tapes” (Reapproved 2011) with testing conducted at 70℃. The adhesive was laminated to primed 0.002 inch (51 micrometers) polyester film. Tape samples measuring 25.4 millimeters (1.0 inches) by 15.2 centimeters (6.0 inches) were cut. The tape samples were then applied to a stainless steel panel previously wiped clean with methyl ethyl ketone (MEK) , then acetone, then n-heptane using lint free tissues. The samples were then centered on the panels and adhered to one end such that tape overlapped the panel by 25.4 millimeters (1 inch) in the lengthwise direction.

The tape sample was then rolled down twice in each direction using a 2 kilograms (4.4 pounds) rubber roller at 12 inches/minute. The free end of the tape was folded over and adhered to itself such that there was no exposed adhesive. This free end was folded over and around a hanging hook and stapled together to secure the hook in place. The resulting panel /tape /weight assembly was suspended vertically in a stand at an angle of 2 degrees to ensure a shear failure mode in a 70℃ chamber. After 10 minutes of temperature equilibration, a 1.0 kilogram (2.2 pounds) weight was attached to the hook and the time, in minutes, for the tape to fall from the panel was recorded. The test was terminated as qualified if failure had not occurred by 1,000 minutes and the result recorded as “＞1,000” . The test was continued and terminated as excellent if failure had not occurred by 10,000 minutes and the result recorded as “＞10,000” . The average for two samples was reported.

Shear Adhesion Strength at 70℃ with 500 gram Weight

This test is the same as the Shear Adhesion Strength at 70℃ with 1000 gram Weight, excpet the 1000g weight si replaced with a 500g weight. This test is employed with very thin substrates, such as PEEK film. PEEK film is often thin (5-9 um) and can not withstand the 1000g weight in a shear test. Instead of actually testing for adhesive or cohesive failure, the 1000g weight on PEEK at 70C frequently tears the PEEK, nullifying the test. A 500g weight at 70C with an adehsive on PEEK is adequate to test the shear resistance of the adhesive.

Glass Transition Temperature

The glass transition temperature of cured silicone adhesive compositions prepared in the following embodiments and comparative example is measured by the following method. The glass transition temperatures defined by the present invention are all based on rheological data, where the temperature corresponding to the maximum value of the loss factor (or tan delta) is taken as the glass transition temperature.

The rheological curve properties of cured silicone adhesive compositions prepared in the following embodiments and comparative examples are measured respectively by the following method.

Dynamic Mechanical Analysis (DMA)

Dynamic mechanical analysis was used to measure the storage modulus and glass transition temperatures of adhesives. A rheometer (Model DHR-2 or ARES-M, TA Instruments, New Castle, DE) having parallel top and bottom plates, each having a diameter of 8 millimeters was used. An adhesive sample in the form of a circular disk having a diameter of 8 millimeters and a thickness of approximately 1 millimeter was transferred onto the bottom plate of the rheometer. For the DHR-2 rheometer, the procedure was as follows: the sample was mounted between the parallel plates, conditioned at -40℃ for 3 minutes, then underwent a temperature oscillation ramp (at a rate of 3℃/minute, at a frequency of 1 Hertz, and an initial strain amplitude of 2%with autostrain enabled) from -40℃ to 50℃, then underwent a temperature oscillation ramp (at a rate of 3℃/minute, at a frequency of 1 Hertz, and an initial strain amplitude of 5%strain from 50℃ to 200℃ or 250℃) before finally cooling to room temperature.

Select samples were tested while being heated from -40℃ to 250℃ all other parameters the same. Storage modulus (G’) and Loss Modulus (G” ) data were collected over the entire temperature range and reported in Pascals. Tan delta was calculated as the ratio of (loss modulus/storage modulus) = (G” /G’) . The temperature at which the tan delta curve exhibited a local peak was reported as the glass transition temperature (Tg) in ℃. G’ and tan delta at various temperatures including the minimum tan delta are reported in the tables.

FIG. 1 is a graph presenting dynamic mechanical anlysis data measured for Example 1. Line A represents G’ and line B represents G” , both referencing the left-hand scale. Line C represents tan delta, referencing the righ hand scale. (1 dyn/cm ²= 0.1 Pa)

In the temperature sweep rheology (1 Hz) of Example 1 shown above, the maximum of the loss tangent (or tan delta) is at -24.8 ℃, which is defined as the Tg. The height of the tan delta curve is 1.1 at Tg and this is defined as TDmax. The minimum of the tan delta curve over the range -40℃ to 200 ℃ is 0.42 and is defined as TDmin. The value of tan delta at 200℃ is 0.46 and is defined as TD200. In some cases, the minimum value of tan delta occurs at 200℃, in which case the TDmin and the TD200 have the same value. The value of the storage modulus at 25℃ is 3.5 E+04 Pa and is defined as G’25. The change in tan delta between the minimum value and the value at 200℃ is obtained by subtraction of the value TD200minus the value at TDmin which in this example is 0.46-0.42=0.04. Common rheometers and software, such as the TA Instruments DHR-2 rheometer and TRIOS software, are capable of establishing master curves for presure sensitive adhesives. Through time temperature superposition principles, temperature sweeps of an adhesive at a variety of frequencies can be used to calculate shift factors and ultimately generate a master curve at room temperature, which provides the rheology of the adhesive at 25℃ over a wide range of frequencies. As the loss factor curve (or tan delta) is key to the damping properties of the adhesive, the master curve (MC) provides a way to evaluate adhesives ability to dampen the frequencies of interest for microspeakers (typically 100-1000 Hz) . The frequency at which the tan delta curve has a maximum value is defined as the MCmax frequency and the height of the tan delta curve of the master curve tan delta curve at that frequency is defined as the MC TDmax. FIG. 2 is the 25℃ master curve of example 1, it can be seen that the MC TDmax was 1.03 and the MC max freq was 570 Hz.

Materials

NMR Analysis of siloxanes, PSAs, and catalyst for equivalent weight and composition

PDV-1641, PDV-0541, and VGP-061 received from Gelest were analyzed for composition and equivalent weight.

PDV-1641 was also found to be a copolymer of dimethyl-siloxane-co-diphenyl siloxane with terminal vinyl dimethylsilyl groups. The molar ratio of dimethylsiloxane to diphenyl siloxane is 83.4: 17.6. The mass ratio of dimethylsiloxane to diphenyl siloxane is 65.4: 34.6. The vinyl equivalent weight was found to be 21100 g/equivalent.

PDV-0541 was found to be a copolymer of dimethyl-siloxane-codiphenyl siloxane with terminal vinyl dimthylsilyl groups, as illustrated below on the right. The molar ratio of dimethylsiloxane to diphenyl siloxane is 94.52: 5.48. The mass ratio ofdimethylsiloxane to diphenyl siloxane is 86.6: 13.4. The vinyl equivalent weight was found to be 18400 g/equivalent.

VGP-061 was found to consist of a dimethylsiloxane-co-diphenylsiloxane-co-vinylmethyl siloxane in a molar ratio of 93.86: 5.99: 0.15 with terminal trimethylsilyl groups. The mass ratio is 0.155 mass %vinylmethyl, 13.99 mass%diphenyl, 85.85 mass %dimethyl and the vinyl groups are internal (or pendant) , not on the terminal groups of the siloxane. Vinyl methyl siloxane groups have a vinyl group and a methyl group on a silicone atom as is illustrated below at left. The vinyl equivalent weight was found to be 55297 g/equivalent. KCT009AC was received and analyzed for composition and for equivalent weight. The results are presented not including the solvent, to reflect the composition of the material used in the dried adhesives formulated as examples and comparative examples.

The analysis found the composition to be 55.1%tackifier (from M, Q3 and Q4 groups) and 44.9%of a gum, consisting of a copolymer of methylvinyl siloxane-co-dimethyl siloxane-co-diphenyl siloxane. Normalizing to 100, the molar ratio was 0.064: 93.77: 6.17 for vinylmethylsiloxane: dimethylsiloxane: diphenyl siloxane in the gum and the mass ratio was 0.07: 84.93: 15.00. As was found in the analysis of VGP-061, the vinyl groups are located at internal positions of the silicone gum, not at terminal positions. The tackifier was also absent of vinyl groups. The equivalent weight of the vinyl groups in the gum alone was 127467. The equivalent weight of the vinyl groups in the dried adhesive was 284049 g/equivalent.

Examples and Comparative Examples

Example 1

A coating solution was prepared by adding the following materials to a MAX 100 SPEEDMIXER cup (FlackTek, Incorporated, Landrum, SC) : 36.0g solution of ShinEtsu KCT-009-AC (61.1%solids) and 13.33g of a 30%solids solution of VGP-061 in toluene. These were mixed two times at 3000 rpm for 1 min in a DAC 150.1 FVZ-K Speed-mixer (FlackTek Inc, Landrum, SC) . A 45%solids solution was obtained.

The solution was coated on the release treated side of a fluorosilicone liner SF 88001, using a notchbar coater having a gap setting of 0.004 inches (101.6rrm) at a speed of 5 fpm. After 20-30 seconds of drying in air, the adhesive coated release liner was taped to a rectangular aluminum frame and the hand-spread was placed in oven at 130℃ (266°F) for 4 minutes.

An adhesive transfer tape having an adhesive layer with a thickness of approximately 30 micrometers on a release liner was obtained.

The sample was submitted for electron beam curing at 200kV and 1.8 MRad.

Example 2

Repeated Example 1, but with the following modification: e-beam irradiation was performed at 2.2 Mrad.

Example 2-A

Example 1 was repeated with the following modifications: the weight of VGP-061 solution was 13.34g and the e-beam irradiation was at 2.4 Mrad.

Example 2-B

Example 2-A was repeated with the following modifications: a fluorinated release solution was prepared by adding the following materials to a MAX 60 SPEEDMIXER cup (FlackTek, Incorporated, Landrum, SC) : 25g of Dowsil Q2-7785, 0.80 g Dowsil Q2-7560 and 74.2 g heptane. These were mixed at 3000 rpm for 1 min in a DAC 150.1 FVZ-K Speed-mixer (FlackTek Inc, Landrum, SC) . A sheet of 9 um PEEK was attached to a piece of polyester, to provide support for the PEEK. The solution was coated on the supported 9 um PEEK, using a notchbar coater having a gap setting of 0.004 inches (101.6μm) at a speed of 5 fpm. After 20-30 seconds of drying in air, the flurosilicone PEEK with support layer was taped to a rectangular aluminum frame and the hand-spread was placed in oven at 130℃ (266°F) for 1 minute. The coating was approximately 20 um thick. A black Sharpie marking pen was used to mark the PEEK that was coated with the fluorosilicone. The ink beaded up and qcould easily be removed with a cotton wipe, thus confirming the presence of the fluorosilicone coating.

The dried fluorosilicone coated PEEK layer was laminated to the surface of the damping adhesive of E3 with the fluorinated surface in contact with the adhesive. The sample was e-beamed through the PEEK layer with 2.4 Mrad after which the fluorosilicone PEEK was removed from the adhesive and the adhesive was submitted for rheology.

Example 2-C

Example 2-A was repeated with the following modifications: 9 um PEEK as received from the manufacturer was laminated to the surface of the adhesive. The sample was e-beamed through the PEEK with 2.4 Mrad. The SF88001 liner was removed and the adhesive with 9 um PEEK was subjected to the 70℃ shear test with a 500 g weight. The PEEK was firmly attached to the adhesive. Only shear property has been tested for E2-C, since it is on PEEK. The fluorosilicone PEEK of E2-B and E2-C are the same PEEK with the same thickness. It is predicable that the rheology of E2-B and E2-C are the same.

Example 3

Repeated Example 1, but with the following modification: e-beam irradiation was performed at 2.6 Mrad.

Example 4

A coating solution was prepared by adding the following materials to a MAX 100 SPEEDMIXER cup (FlackTek, Incorporated, Landrum, SC) : 13.8g solution of a 70%solids solution of Dowsil 2-7066 and 33.33g of a 30%solids solution of VGP-061 in toluene. These were mixed at 3000 rpm for 1 min twice in a DAC 150.1 FVZ-K Speed-mixer (FlackTek Inc, Landrum, SC) . A 41.6%solids solution was obtained.

The solution was coated on the release treated side ofa fluorosilicone liner SF 88001, using a notchbar coater having a gap setting of 0.004 inches (101.6μm) at a speed of 5 fpm. After 20-30 seconds of drying in air, the adhesive coated release liner was taped to a rectangular aluminum frame and the hand-spread was placed in oven at 130℃ (266°F) for 4 minutes. An adhesive transfer tape having an adhesive layer with a thickness of approximately 30 micrometers on a release liner was obtained.

The sample was submitted for e-lectron beam curing at 200kV and 1.8 Mrad.

Example 5

Repeated Example 4, but with the following modifications: E-beam irradtion was perfromed at 2.2 Mrad.

Example 6

A coating solution was prepared by adding the following materials to a MAX 100 SPEEDMIXER cup (FlackTek, Incorporated, Landrum, SC) : 36.0g solution of ShinEtsu KCT-009-AC (61.1%solids) , 8.33g of a 30%solids solution of VGP-061 in toluene, 1, 51g PDV-0541, and 5.09g toluene. These were mixed two times at 3000 rpm for 1 min in a DAC 150.1 FVZ-K Speed-mixer (FlackTek Inc, Landrum, SC) . A 51%solids solution was obtained.

The solution was coated on the release treated side of a fluorosilicone liner SF 88001, using a notchbar coater having a gap setting of 0.004 inches (101.6μm) at a speed of 5 fpm. After 20-30 seconds of drying in air, the adhesive coated release liner was taped to a rectangular aluminum frame and the hand-spread was placed in oven at 130℃ (266°F) for 4 minutes. An adhesive transfer tape having an adhesive layer with a thickness of approximately 33 micrometers on a release liner was obtained.

The sample was submitted for electron beam curing at 200kV and 1.8 Mrad.

Example 7

A coating solution was prepared by adding the following materials to a MAX 100 SPEEDMIXER cup (FlackTek, Incorporated, Landrum, SC) : 36.0g solution of ShinEtsu KCT-009-AC (61.1%solids) , 8.33g of a 30%solids solution of VGP-061 in toluene, 1.51g PDV-1641, and 5.08g toluene. These were mixed two times at 3000 rpm for 1 min in a DAC 150.1 FVZ-K Speed-mixer (FlackTek Inc, Landrum, SC) . A 51%solids solution was obtained.

The solution was coated on the release treated side ora fluorosilicone liner SF 88001, using a notchbar coater having a gap setting of 0.004 inches (101.6μm) at a speed of 5 fpm. After 20-30 seconds of drying in air, the adhesive coated release liner was taped to a rectangular aluminum frame and the hand-spread was placed in oven at 130℃ (266°F) for 4 minutes. An adhesive transfer tape having an adhesive layer with a thickness of approximately 33 micrometers on a release liner was obtained. The sample was submitted for electron beam curing at 200kV and 4.5 Mrad.

Comparative Example 1

Repeated Example 4, but with the following modification-: E-beam irradiation was perfomed at 3.0 Mrad.

Comparative Example 2

A coating solution was prepared by adding the following materials to a MAX 100 SPEEDMIXER cup (FlackTek, Incorporated, Landrum, SC) : 65.76g of a 19.5%solids solution of Dehesive 948 and 11.85g of T803 MQ powder. These materials were mixed three times at 3000 rpm for 1 min in a DAC 150.1 FVZ-K Speed-mixer (FlackTek Inc, Landrum, SC) . A 31.8%solids solution was obtained.

The solution was coated on the release treated side of a fluorosilicone liner SF 88001, using a notchbar coater having a gap setting of 0.006 inches (126.6μm) at a speed of 5 fpm. After 20-30 seconds of drying in air, the adhesive coated release liner was taped to a rectangular aluminum frame and the hand-spread was placed in oven at 130℃ (266°F) for 4 minutes. An adhesive transfer tape having an adhesive layer with a thickness of approximately 30 micrometers on a release liner was obtained.

The sample was submitted for electron beam curing at 200kV and 1.8 Mrad.

CE2 was made with a blend of (solids ratio) 47.5%T803 MQ and 52.5%Wacker Dehesive 948, a vinyl terminated polydimethylsiloxane.

Comparative Example 3

A coating solution was prepared by adding the following materials to a MAX 100 SPEEDMIXER cup (FlackTek, Incorporated, Landrum, SC) : 28.81g solution of ShinEtsu KCT-009-AC (61.1%solids) and 2.64 of PDV-0541 and 12.03g toluene. These were mixed two times at 3000 rpm for 1 min in a DAC 150.1 FVZ-K Speed-mixer (FlackTek Inc, Landrum, SC) . A 47%solids solution was obtained.

The solution was coated on the release treated side of a fluorosilicone liner SF 88001, using a notchbar coater having a gap setting of 0.004 inches (101.6μm) at a speed of 5 fpm. After 20-30 seconds of drying in air, the adhesive coated release liner was taped to a rectangular aluminum frame and the hand-spread was placed in oven at 130℃ (266°F) for 4 minutes.

The sample was submitted for electron beam curing at 200kV and 7.0 Mrad.

In the following tables, “CE” means Comparative Example and “E” means Example. Table 1 represents the cured silicone adhesive composition content of the Examples and Comparative Examples. Percentages were weight percent based on total weight of cured silicone adhesive composition.

The absolute value of the minimum tan delta in a temperature range of 25 ℃ to 200℃ (Tdmin) and the tan delta at 200℃ (TD200) indicate how silicone adhesive dampens at higher temperatures compared to another, where higher is better. But TD200 should be lower than 0.9 to aviod poor shear performance.

El with diphenyl and a lower amount of electron beam dose crosslinking has good damping performance at high temperature and good sheer result of 25,000 minutes.

E7, with total diphenyl content of 9.06%and a higher amount of electron beam dose of 4.5 Mrad, has a qualified damping performance at high temperature and good sheer result of 4500 minutes. Compared to E4, CE1 is over-crosslinked with too much e-beam than E4, it has good sheer performance at high temperature, but the damping is much less, Tdmins is less than 0.27.

CE2 was made with a blend of a tackifier and a vinyl terminated polydimethylsiloxane without diphenylsiloxane units. CE2 has a tan delta of less than 0.27, it has unqualified damping performance and sheer performance at high temperature is qualified.

CE3 is over-crosslinked with too much e-beam, it has good sheer performance at high temperature, but the damping is much less, Tdmins is far less than 0.27 which has to a poor high temperature damping property.

The embodiments of the present invention described above are merely illustrative of the preferred embodiments of the present invention, and are not intended to limit the concept and scope of the present invention. Various modifications and improvements can be made to the technical solution of the present invention by those skilled in the art without departing from the scope of the present invention, which are all embraced in the protection scope of the present invention as defined by appended claims.

Claims

A cured silicone adhesive composition, comprising a chemically cross-linked reaction product of the following reaction components:

an optional vinyl functional siloxane having a vinyl functionality of 2 or more and diphenylsiloxane units;

a siloxane gum comprising diphenyl siloxane groups, and vinylalkyl siloxane groups;

an effective amount of a tackifier;

wherein the total weight percentage of diphenylsiloxane units is 6%to 11%, according to the formula -Si (Ph) ₂-O-, based on the total weight of the cured silicone adhesive composition, the cured silicone adhesive composition has a tan delta of at most 0.9 for a temperature equal to 200℃, and the cured silicone adhesive composition has a tan delta of at least 0.27 in a temperature range from 25℃ to 200℃, as measured by a rheological curve.
A cured silicone adhesive composition according to claim 1, wherein the cured silicone adhesive composition has a tan delta of at least 0.35 in a temperature range from 25℃ to 200℃, as measured by a rheological curve.
A cured silicone adhesive composition according to claim 1, wherein the siloxane gum comprises 11-17 mass percentages of diphenyl siloxane groups, 82-89 mass percentages of dimethyl siloxane groups, 0.02-0.2 mass percentages of vinylmethyl siloxane groups and vinyl equivalent weights of 50,000 to 200,000.
A cured silicone adhesive composition according to claim 1, wherein the vinyl functional siloxane includes divinyl terminated polydimethylsiloxane-co-diphenyl siloxane with 10-40 mass percentages of diphenyl groups, 60-90 mass percentages of dimethyl groups and vinyl equivalent weights of 3000-25000 g/eq.
A cured silicone adhesive composition according to claim 1, wherein the vinyl functional siloxane includes dimethyl siloxane-co-diphenyl siloxane-co-vinylmethyl siloxane, wherein the vinylfunctional siloxane comprises 11-17 mass percentages of diphenyl siloxane groups, 82-89 mass percentages of dimethyl siloxane groups, 0.02-0.20 mass percentages of vinylmethyl siloxane groups and vinyl equivalent weights of 30,000 to 200,000
A cured silicone adhesive composition according to claim 1, wherein the tackifier comprises a silicone tackifier comprising MQ resins.
A cured silicone adhesive composition according to claim 1, wherein the cured silicone adhesive composition has shear adhesion strength at 70℃ with 1000 gram weight, on stainless steel, of 1,000 minutes or more.
A cured silicone adhesive composition according to claim 1, wherein the glass transition temperature of the cured silicone adhesive composition is -10℃ to -36℃.
A cured silicone adhesive composition according to claim 1, wherein the glass transition temperature of the cured silicone adhesive composition is -14℃ to -31 ℃.
A cured silicone adhesive composition according to claim 1, wherein the chemically cross-linked reaction product is cross-linked by radiation.
A cured silicone adhesive composition according to claim 10, wherein the chemically cross-linked reaction product is cross-linked by radiating electron beam.
A damping film used for microspeaker, wherein the damping film comprises a cured silicone adhesive composition according to any one of claim 1 to 11.
A damping film used for microspeaker according claim 12, wherein the thickness of the damping film is 5 to 50 micrometers.
A damping film used for microspeaker according claim 12, wherein the thickness of the damping film is 10 to 40 micrometers.
A diaphragm used for microspeaker having multilayer laminate construction, wherein the diaphragm comprises a damping film according to claim 12.
A diaphragm according to claim 15, wherein the diaphragm further comprises at least a stiff layer.
A diaphragm according to claim 16, wherein the stiff layer comprise a material whose principal constituent is selected from the group consisting of: polyethylene terephthalate (PET) , polycarbonate (PC) , polybutylene terephthalate (PBT) , polyethylene naphthalate (PEN) , polyetheretherketone (PEEK) , polyetherketone (PEK) , polyetherimide (PEI) , polyimide (PI) , polyarylate (PAR) , polyphenylene sulfide (PPS) , polyphenylsulfone (PPSU) , polysulfone (PSU) , polyethersulfone (PES) , polyurethane (PU) , and liquid crystal polymer (LCP) .
A method of manufacturing a damping film used for microspeaker, the damping film comprising a cured silicone adhesive composition and an optional stiff layer, the method comprises a chemical crosslinking treatment to a reaction product of the following reaction components by radiation:

an optional vinyl functional siloxane having a vinyl functionality of 2 or more and diphenylsiloxane units;

a siloxane gum comprising diphenyl siloxane groups, and vinylalkyl siloxane groups;

an effective amount of a tackifier;

wherein the total weight percentages of diphenylsiloxane units being 6%to 11%, according to the formula -Si (Ph) ₂-O-, based on the total weight of the cured silicone adhesive composition, and the cured silicone adhesive composition has a tan delta of at most 0.9 for a temperature equal to 200℃, and the cured silicone adhesive composition has a tan delta of at least 0.27 in a temperature range from 25℃ to 200℃, as measured by a rheological curve.
The method of manufacturing a damping film used for microspeaker according to claim 18 wherein the chemical crosslinking treatment comprises crosslinking the reaction product by radiating electron beam.
The method of manufacturing a damping film used for microspeaker according to claim 19, wherein the chemical crosslinking by radiating electron beam comprises radiating the reaction product using an electron beam having electron beam energy of 100 to 300 KV for an electron beam dose of 1.2 Mrad to 4.5 Mrad.
The method of manufacturing a damping film used for microspeaker according to claim 18, wherein the stiff layer comprise a material whose principal constituent is selected from the group consisting of: polyethylene terephthalate (PET) , polycarbonate (PC) , polybutylene terephthalate (PBT) , polyethylene naphthalate (PEN) , polyetheretherketone (PEEK) , polyetherketone (PEK) , polyetherimide (PEI) , polyimide (PI) , polyarylate (PAR) , polyphenylene sulfide (PPS) , polyphenylsulfone (PPSU) , polysulfone (PSU) , polyethersulfone (PES) , polyurethane (PU) , and a liquid crystal polymer (LCP) .